Amal Clooney

She said in a letter to foreign secretary Dominic Rabb that she was “dismayed to learn that the government intends to pass legislation – the Internal Market Bill – which would, by the government’s own admission, break international law if enacted.”

She said it is “lamentable for the UK to be speaking of its intention to violate an international treaty signed by the prime minister less than a year ago.”

Ms Clooney added that she had been given “no assurance that any change of position is imminent” and as a result “it has become untenable for me, as Special Envoy, to urge other states to respect and enforce international obligations while the UK declares that it does not intend to do so itself.”

Sir Keir Starmer, Labour leader and formerly a barrister at the same chambers as Ms Clooney, told the BBC: “I know Amal and she is a first class lawyer. I’m not surprised that she has quit because, like others, she’s concluded that there is a conflict between a breach of international law - which the government seems intent on - and our reputation as a country in the world that abides by the rule of law.”

Her resignation comes days after Lord Keen left the government also in response to its approach to the Brexit withdrawal agreement.